1. Field of the Invention
The present invention relates generally to equipment for the thermal spraying of powdered materials. More specifically, the present invention relates to a cathode interface for use with a thermal spray plasma gun.
2. Description of Related Art
A variety of thermal spray coatings have been used to protect various types of components. Coatings may provide various benefits such as to resist wear, retard corrosion, control clearances, salvage worn components, resist high temperatures and/or enhance electrical properties. These benefits can differ based on the coating material type and how those materials are applied. One group of spray coatings to which the subject matter of the present invention pertains in particular are those applied via the plasma spray process. This process has been used to apply many different types of coatings in numerous industries.
Each material coating specification requires a specific range of velocity and temperature transferred to the powder particle to achieve the required material properties on the part Improved consistency and efficiency in the delivery of thermal spray coatings remains an industry-wide goal.
The plasma gun has been used as a process tool in the spray coatings industry due to the wide range of parameters that are achievable with this basic tool. A key element of any plasma gun is the cathode geometry. Variations in cathode geometry can allow a plasma gun to provide coating properties at a different temperatures and velocities from the same base equipment. During repeat use, cathode exhibit wear which leads to replacement of the part. Thus a single plasma gun typically required replacement of the cathode. Prior art configurations were such that replacement of the cathode was difficult and took a long time, leading to long down times when the part needed to be replaced.
However, there are a number of factors that can prove challenging in replacing the a plasma gun cathode. Plasma spray guns must perform several different functions in order to achieve a successful coating process. Those functions include proper alignment of the cathode as well as cooling of the gun cathode during the spray process to prevent overheating. Accordingly proper flow of coolant sealing around the cathode area and adequate sealing of the cooling path is needed. An electrical connection between the cathode and the plasma gun is also required to serve as the return path for the plasma arc current flow. Precise orientation of mechanical location, electrical connections and water chamber seals must be achieved to obtain the desired gun operation and gun characteristics.
FIGS. 1 and 2 show one example of a known plasma gun 1 (only the certain main portions of the gun are shown for purposes of illustration) that has a replaceable cathode 10. As can be readily seen, the cathode 10 has a mounting portion 20 and a tip 30 from whose front end 32 a plasma arc discharges in a continuous manner during plasma spraying. The tip 30 typically has a rear portion 31 that is fixed to and extends into a receiving zone 24 of the mounting portion 20. The mounting portion 20 includes a main internal space 21 which is sized and configured to receive therein cooling fluid and accommodates therein a front portion of a cooling tube 40. Cooling fluid passes through the tube 40 via a main cooling passage 70 of the plasma gun 1. The mounting portion 20 also includes an external thread 22 which threads into comparable internal threads of the component 50 and functions to axially mechanically fix and electrically connect the cathode 10 to a main internal component 50 of the plasma gun 1. However, to provide sealing between the cathode 10 and the component 50 to among other things, prevent cooling fluid (typically pressurized) from escaping from the space 21, a seal or O-ring 60 is typically provided in an area of an annular connecting interface 23. Owing to its position in the interface 23, the O-ring 60 is subjected to relatively high temperatures. Additionally, its location in the interface 23 is not ideal from the standpoint of providing maximum electrical conductivity between the cathode 10 and the component 50. As such, providing a standardized interface which would offer significant improvement over known connecting interfaces between these components should take these considerations into account.
Utilizing a standard interface in a plasma gun has been utilized in areas such as the nozzle interface. U.S. Pat. No. 7,759,599 to HAWLEY et al., for example, describes one such arrangement, the disclosure of which is hereby expressly incorporated by reference thereto in its entirety. However, providing a standard interface for a cathode of a plasma gun has unique challenges which are not addressed by this document.
A standard interface for each cathode that would assure proper orientation of all plasma gun components with each interchangeable cathode, while minimizing the risk of human error would be beneficial to the spray coating industry. Optimal orientation could extend the range of performance for a single thermal spray plasma gun. Thus, there remains a need in the art for a standard cathode interface for a thermal spray plasma gun that provides an optimal, efficient and repeatable cathode connection for a wide range of cathode geometries.